American Heritage Dictionary:
n. An enticing plea or appeal, especially one that is deceptively alluring.
the enticing appeal of something alluring but potentially dangerous
Alaska Airlines Insider, July 3, 2007:
"Heed the siren song of Canada, from Victoria to Edmonton. And, if you travel between September 5 and November 15, 2007, you can save 20 percent on travel—on all points Alaska and Horizon fly across the western Provinces."